This invention relates to pollution detection. Specifically, this invention relates to a system and method for automated remote detection and reporting of subterranean pollutants in liquid and gaseous form.
Environmentally harmful chemicals are commonly utilized in industrial and commercial processes. Similarly, chemical wastes are commonly stored in man made storage tanks, containers and reservoirs. Although precautionary measures and controls such as impermeable liners are generally used, leaks or spills from such systems are common, resulting in migration of harmful materials into the subsurface soil and groundwater. Many release events go unidentified by the property owner and are not discovered until contaminants have spread a considerable distance from the source. Such pollution scenarios can result in property devaluation, regulatory compliance issues, legal challenges, and costly remediation requirements. Early detection and response to such spills and leaks can substantially reduce liabilities to such property owners.
In the past, environmental monitoring systems have been devised to detect leaks and fugitive emissions from various storage systems, processes, and conduits. Many such methods offer means of detecting release events, however there are presently no known efficient methods employed for, remote, real time monitoring of chemical releases to the subsurface. In particular there is no known means of automated remote, real-time monitoring for early detection of low level concentrations of volatile organic compounds (VOCs) associated with commercial facilities such as dry cleaners, printers, and automotive servicing facilities.
Without the means of continuous remote monitoring, it is the current practice to detect and quantify potential subsurface contamination by means of cumbersome investigative and subsurface sampling techniques that requires both onsite sampling and off-site analytical testing for contaminants and their concentrations.
There have been systems devised for environmental monitoring of fugitive chemical emissions from piping, as described in xe2x80x9cReversible Sensor for Detecting Solvent Vapors,xe2x80x9d U.S. Pat. No. 5,417,100 issued to Miller, et al. Similarly there are methods for measuring in line process gases, as described in xe2x80x9cContinuous Monitoring of Organic Pollutants,xe2x80x9d U.S. Pat. No. 5,435,169 issued to Mitra. However, such methods were not developed or applied to the monitoring of chemical migration to the subsurface environment.
Additionally, leak detection methods, as described in xe2x80x9cSystem for Detecting Leaks from Liquid-Containing Reservoirs and Conduits,xe2x80x9d U.S. Pat. No. 4,404,516 issued to Johnson, have been devised for monitoring storage tanks and reservoirs. However, those methods are limited to on-site systems that require facility operator response.
Other environmental monitoring systems have been devised for monitoring of chemical fugitive emissions at large industrial facilities. One such system, as described in xe2x80x9cSoil Pollution Monitoring System,xe2x80x9d U.S. Pat. No. 4,618,855 issued to Harding, et al., actively pumps gases from the subsurface of the facility past a sensing device in order to detect the presence of vapor. This system relies on a vacuum pump to draw air and leakage gases through the ports and past sensors which detect the presence of gasoline, carbon monoxide, methane, ethanol, and other vapors. Accordingly, a ducting mechanism is required to force fresh air by the sensors periodically so as to clean the sensors before a new reading can be taken.
Environmental monitoring systems, as described in xe2x80x9cEnvironment Monitoring System,xe2x80x9d U.S. Pat. No. 5,892,690, issued to Boatman, et al., utilize a data acquisition system for collecting and recording air quality data from remote locations. The data is accumulated and stored into a comprehensive database.
However, existing methods are not designed to monitor multiple facilities from a remote location with the capability of real-time detection of subterranean pollutants coupled with immediate notification to a third party of such a detection.
The present invention addresses these and other problems.
The present invention provides a system and method for automated remote real-time detection and reporting of subterranean chemical pollutants. The system is provided as part of a remote real time pollution detection and reporting service, particularly for customers owning, or responsible for, property where volatile organic compounds (VOC) are stored or utilized.
The system of the present invention includes a series of sensors placed in strategically located underground cavities beneath a property to detect chemical contamination caused by the release of chemical pollutants into the subsurface soil and groundwater. The relative placement of the sensors is determined by a number of factors. These factors include the rate of vapor flow diffusing through the native soil of the property, the volatility of the particular chemicals likely to be released on the property, and the location of likely sources of the chemical contaminants. These and other factors are well known in the art, and have been utilized in the past for determining the locations for collection of representative samples.
In accordance with one aspect of the invention, the sensors are housed within a perforated housing seated within a cavity beneath the surface of a property. The cavity functions as a mass flux chamber in order to maximize sensor response. The cavity is filled with a high porosity media, so as to provide separation between the native soil and the sensors, while minimizing resistance to the migration of chemical vapors to the sensors. Additionally, the high porosity media increases the surface area of contact between the subsoil and the sensors. The high porosity media may be glass or sand, although other materials well known in the art may be used in the alternative. The mass flux cavity facilitates the detection of the rate of change in concentrations of vapors migrating by diffusion through the soil environment.
In another aspect of the invention, a semi-permeable membrane surrounds the perforated housing. The membrane is utilized when the sensors are required to be placed in a moist or wet subsurface, for example in an area having a high water table. The membrane prevents liquids, such as water from penetrating through the housing into the sensor, while still allowing chemical vapors to pass through. This protection is necessary since liquid contact with the sensors may also skew any readings made by the sensors, and thus affect the accuracy of the chemical detection.
In a preferred embodiment, there are multiple sensors housed as an array within each perforated housing. The type of sensors used may vary, but are preferably of the type known as surface acoustic wave (SAW) sensors. A SAW sensor is a mass sensitive sensor that transmits an electric signal at a frequency which is effected by the presence of a particular chemical or chemicals. When a change in mass occurs at the surface of the sensor, the frequency of the signal changes accordingly. Among the SAW sensors contained in the array may be a reference sensor having a fixed operating frequency in the range of 100 MHz to 400 MHz. The remaining SAW sensors are selectively coated so as to react to various chemical vapors likely to be detected in the event of a leak on the property. The chemical selectively forms a weak bond to the coating in a process known in the art as sorption. Each sensor has a normal operating frequency, determined by the characteristics of the coating utilized. As a particular chemical vapor travels across the sensor, it attaches to the selective coating, changing the effective mass of the coating, which in turn alters the operating frequency of the sensor.
An important benefit of SAW sensors is their durability and reliability. Their operating frequencies and responses are initially set by a photolithographic process. The photolithographic process is a process known in the art for producing integrated circuits and printed circuit boards by photographing the circuit pattern on a photosensitive substrate and then chemically etching away the background. The SAW sensor frequency is generated at the site by oscillator circuits. As such, these sensors do not require tuning operations nor do they become de-tuned in the field. Additionally, the sorption process allows the sensor to be reusable, as the weak bonds formed with the chemical are easily broken by the introduction of heat. Thus the sensor is capable of functioning as a reusable event detector.
The composite acoustic response of the sensor array can be likened to a fingerprint. SAW sensors fall under the category of xe2x80x9csmart sensorsxe2x80x9d that are capable of identifying the specific components as well as the concentration of a particular chemical within a sample. Conventional detectors, such as metal oxide semi-conductors, produce a broad response to a class of chemicals and physical conditions. In practice, conventional detectors alone often give false positive detection readings of a chemical leak. Consequently, an on-site visit and chemical analysis is required to confirm the reading. The use of SAW sensors facilitates the reliable and automated remote detection of specific chemical pollutants in a subsurface described in the present invention.
The preferred embodiment also includes an onsite computer processor connected to the various sensor arrays, which acts as a sensor interface. The computer processor has embedded within it software capable of reading the acoustic response, or fingerprint, of the SAW sensors. Additionally, a database is accessible by the software for identifying the specific sensor fingerprint of the chemical being detected by the sensor. The database may be stored within a data storage device housed within the computer, or be located on a remote computer, accessible by various means including the Internet. As such, the computer processor connects to a remote server computer, located at a remote monitoring station, that receives data from the onsite processor and may automatically report detection of a chemical release to a designated party. The software also provides a means for calibrating the sensors, performing functional status checks, and setting appropriate response thresholds from the remote server.
An important benefit of the onsite computer processor integrated with a remote server is the capability of continuous and automated monitoring of the property from a remote location. The utilization of a sensor array having SAW sensors, or a similar sensor device, in combination with a computer processor eliminates the need for onsite visits to the property to take samples from alternate sensing devices, which would usually require an offsite laboratory analysis.
The use of a remote monitoring station allows for immediate and automated monitoring of various sensor arrays located at multiple properties. When utilized as part of a pollution detection service, the remote monitoring station facilitates the immediate notification to third parties of a chemical pollutant in the subsurface of a property. The third party may be the owner of the property, or another designated entity responsible for responding to a chemical leak. In the preferred embodiment, this notification is provided as part of a subscribed service.
The foregoing has outlined some of the more pertinent objects of the present invention. These objects should be construed to be merely illustrative of some of the more prominent features and applications of the invention. Many other beneficial results can be attained by applying the disclosed invention in a different manner or by modifying the invention as will be described. Accordingly, other objects and a fuller understanding of the invention may be had by referring to the following Detailed Description of the Invention, which includes the preferred embodiment.